考虑软黏土循环弱化效应后超长桩屈曲稳定性分析

Analysis of Buckling Stability of Superlong Piles Considering Cyclic Weakening Effect of Soft Clay

摘要:

超长桩因能适应软基深水条件被广泛应用于外海码头建设之中，然而超长桩由于桩身长度、桩身自由长度均较传统桩基更长，长细比更大，存在屈曲失稳的风险。在波浪、海流等循环荷载作用下，桩侧软黏土会产生强度弱化与刚度衰减的循环弱化效应，进一步加剧了超长桩发生屈曲失稳的风险。鉴于此，首先基于 ABAQUS 有限元软件二次开发平台，借助 USDFLD 子程序并采用 FORTRAN 语言对已有试验获得的软黏土强度弱化与刚度衰减规律计算模型进行数值开发，并将数值计算结果与离心机试验结果进行对比，验证了本研究中所建立的软黏土强度弱化与刚度衰减子程序的合理性与可靠性。然后建立了软基深水超长桩数值计算模型，开展了超长桩屈曲稳定性研究，明确了超长桩发生屈曲失稳的可能性，并进一步研究了单独考虑强度弱化、刚度衰减以及同时考虑强度弱化与刚度衰减后对超长桩屈曲稳定性的具体影响情况。研究结果表明，超长桩屈曲临界荷载值分别降低了 3.5%、 7.9%、11.0%，屈曲失稳时桩身最大剪力分别降低了 3.6%、17.1%、22.1%，表明软黏土循环弱化效应显著增加了超长桩屈曲失稳破坏的风险。研究成果可为同类工程问题研究提供参考借鉴。

Abstract:

Super-long piles are widely used in offshore wharf structures due to their adaptability to soft clay grounds and deep-water conditions. However, given their greater pile length and free length compared to conventional pile foundations, super-long piles have a higher slenderness ratio and are at risk of buckling instability. Under cyclic loading from waves and ocean currents, the soft clay around the pile may experience cyclic weakening effects characterized by strength weakening and stiffness degradation, further increasing the risk of buckling instability in super-long piles. In view of this, this study first developed the calculation model for the strength weakening and stiffness degradation patterns of soft clay, derived from existing experimental data based on the ABAQUS secondary development platform and with the help of USDFLD subroutine and FORTRAN language. The numerical results were then compared with centrifuge test results, validating the rationality and reliability of the established subroutine for soft clay strength weakening and stiffness degradation. Subsequently, a numerical calculation model of super-long piles in deep-water soft clay grounds was established to investigate the buckling stability of super-long piles. This study clarified the possibility of buckling instability and further investigated the specific effects on buckling stability under three scenarios: considering strength weakening alone, stiffness degradation alone, and the combined impact of strength weakening and stiffness degradation. The results showed that the critical buckling load of super-long piles decreased by 3.5%, 7.9%, and 11.0%, respectively, under these three scenarios. The maximum shear force in the pile at buckling instability decreased by 3.6%, 17.1%, and 22.1%, respectively, indicating that the cyclic weakening effect of soft clay significantly increased the risk of buckling instability failure of the super-long piles. The findings can provide a valuable reference for research on similar engineering problems.